U.S. patent number 4,065,544 [Application Number 05/481,321] was granted by the patent office on 1977-12-27 for finely divided metal oxides and sintered objects therefrom.
This patent grant is currently assigned to Union Carbide Corporation. Invention is credited to Bernard H. Hamling, Alfred W. Naumann.
United States Patent |
4,065,544 |
Hamling , et al. |
December 27, 1977 |
Finely divided metal oxides and sintered objects therefrom
Abstract
Finely-divided metal oxides are prepared by the steps of (a)
contacting a compound of a metal with a carbohydrate material to
obtain an intimate mixture thereof, (b) igniting this mixture to
oxidize the same and to insure conversion of substantially all of
said metal compound to a fragile agglomerate of its metal oxide,
and (c) pulverizing the product of step (b) to form a
finely-divided metal oxide powder having a mean particle size below
about 1.0 micron. Certain of the finely-divided metal oxide powders
produced by this process have the useful property of sinterability
at temperatures significantly lower than metal oxide powders
heretofore readily available. The powders are useful in the
preparation of high strength compacted shapes for use in high
temperature and/or corrosive environment, in the preparation of
refractory cements, catalysts, catalysts supports and the like.
Inventors: |
Hamling; Bernard H. (Warwick,
NY), Naumann; Alfred W. (Monsey, NY) |
Assignee: |
Union Carbide Corporation (New
York, NY)
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Family
ID: |
26713179 |
Appl.
No.: |
05/481,321 |
Filed: |
June 20, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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264040 |
Jun 19, 1972 |
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36442 |
May 11, 1970 |
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Current U.S.
Class: |
423/252; 252/625;
423/3; 423/23; 423/53; 423/69; 423/87; 423/99; 423/138; 423/263;
423/608; 264/661; 264/624; 264/.5; 423/21.1; 423/49; 423/62;
423/89; 423/111; 423/155; 423/604; 423/625; G9B/5.267 |
Current CPC
Class: |
C01F
17/224 (20200101); C04B 35/626 (20130101); C01F
17/229 (20200101); G11B 5/70678 (20130101); B01J
37/0018 (20130101); C01B 13/14 (20130101); C04B
35/4682 (20130101); C01G 23/047 (20130101); C04B
35/50 (20130101); C04B 35/48 (20130101); C04B
35/486 (20130101); C04B 35/46 (20130101); C01G
25/02 (20130101); C04B 35/2683 (20130101); C01G
37/00 (20130101); B82Y 30/00 (20130101); C04B
35/26 (20130101); C01B 13/322 (20130101); C01G
23/006 (20130101); C04B 35/51 (20130101); H01F
1/11 (20130101); C01P 2004/50 (20130101); C01P
2004/62 (20130101); C01P 2004/03 (20130101); C01P
2006/13 (20130101); C01P 2002/60 (20130101); C01P
2004/01 (20130101); C01P 2006/33 (20130101); C01P
2002/70 (20130101); C01P 2006/10 (20130101); C01P
2004/64 (20130101) |
Current International
Class: |
A61K
8/43 (20060101); A61K 8/30 (20060101); C01G
25/02 (20060101); C01G 23/00 (20060101); C01G
37/00 (20060101); C01G 23/047 (20060101); B01J
37/00 (20060101); C04B 35/626 (20060101); C04B
35/462 (20060101); C04B 35/486 (20060101); C04B
35/51 (20060101); C04B 35/48 (20060101); H01F
1/11 (20060101); G11B 5/706 (20060101); C04B
35/46 (20060101); C04B 35/50 (20060101); C04B
35/26 (20060101); C01F 17/00 (20060101); C04B
35/468 (20060101); C01G 25/00 (20060101); C01B
13/32 (20060101); C01B 13/14 (20060101); H01F
1/032 (20060101); C01F 015/00 (); C01I 017/00 ();
C01F 007/02 (); C01G 001/02 () |
Field of
Search: |
;264/.5,56 ;252/31.1K
;423/2,3,252,250,260,263,608,604,628,21,23,49,52,62,69,87,89,99,111,138,155,625 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schafer; Richard E.
Attorney, Agent or Firm: Moran; William Raymond
Parent Case Text
This application is a continuation-in-part of U.S. patent
application Ser. No. 264,040 entitled "Finely Divided Metal oxides
and Sintered Objects Therefrom", filed June 19, 1972 by B. H.
Hamling and A. W. Naumann and now abandoned. Ser. No. 264,040 is in
turn a continuation-in-part of Ser. No. 36,442, of the same title
and by the same inventors, filed May 11, 1970, now abandoned.
Claims
What is claimed is:
1. Process for producing finely divided metal oxygen-containing
compounds which comprises:
a. contacting a carbohydrate material with at least one compound of
a metal to form an intimate mixture thereof;
b. introducing said mixture into a heating zone having a
temperature sufficient to ignite said mixture but insufficient to
substantially sinter said metal compound;
c. igniting said mixture in said heating zone for a time period
sufficient to decompose and remove said carbohydrate material and
produce easily disrupted agglomerates of submicron size metal
oxygen-containing particles;
d. disrupting said agglomerates without substantially reducing the
size of the individual particles which comprised said agglomerates
to produce finely divided metal oxygen-containing compounds having
a mean particle size below one micron.
2. The process of claim 1 wherein said carbohydrate material is
cellulosic.
3. The process of claim 1 wherein said carbohydrate material is
wood pulp.
4. The process of claim 1 wherein said carbohydrate material is
cotton.
5. The process of claim 1 wherein said carbohydrate material is a
sugar.
6. The process of claim 5 wherein said sugar is sucrose.
7. The process of claim 5 wherein said sugar is invert syrup.
8. The process of claim 1 wherein said metal oxygen-containing
compound is a metal oxide.
9. The process of claim 1 wherein said metal oxygen-containing
compound is a ferrite.
10. The process of claim 1 wherein said oxygen-containing compounds
are comprised of at least one metal which is selected from the
group consisting of beryllium, magnesium, calcium, the Group III B
metals, the Group IV B metals, niobium, tantalum, the Group VI B
metals, manganese, iron, cobalt, nickel, copper, zinc, cadmium,
aluminum; gallium, tin, lead and bismuth.
11. The process of claim 1 wherein said oxygen-containing compounds
are comprised of at least one metal which is selected from the
group consisting of beryllium, magnesium, calcium, the Group IIIB
metals, the Group IVB metals, niobium, tantalum, the Group VIB
metals, manganese, iron, cobalt, nickel, copper, zinc, cadmium,
aluminum, gallium, tin, lead and bismuth, and at least one
additional metal selected from the group consisting of lithium,
sodium, potassium, rubidium, cesium, strontium, barium, germanium,
vanadium, ruthenium, osmium, rhodium, indium, iridium, thallium and
antimony.
12. Process of claim 1 wherein in step (a), said metal compound
comprises an aqueous solution of a zirconium compound.
13. Process of claim 12 wherein said aqueous solution of a
zirconium compound also contains dissolved therein a compound of a
metal that forms an oxide that stabilizes zirconia.
14. Process of claim 13 wherein said metal that forms an oxide that
stabilizes zirconia is yttrium.
15. Process of claim 12 wherein the zirconia is comminuted by wet
ball milling.
16. Process of claim 12 wherein said aqueous solution of a
zirconium compound also contains dissolved therein at least one
copper and at least one chromium compound that forms an oxide.
17. Process of claim 1 wherein in step (a), said metal compounds
comprise at least one barium and one titanium compound, said
mixture being essentially free of chloride ions.
18. A process for the preparation of submicron barium titanate
powders which process comprises the steps of:
a. contacting a water soluble carbohydrate with an aqueous acidic
solution of a tetraalkyl titanate and an aqueous solution of barium
alkanoate, to form an intimate mixture thereof, said mixture being
essentially free of chloride ions,
b. introducing said mixture into a heating zone having a
temperature sufficient to ignite said mixture but insufficient to
substantially sinter said barium titanate compound;
c. igniting said mixture in said heating zone for a time period
sufficient to decompose and remove said carbohydrate material and
produce easily disrupted agglomerates of sub-micron size barium
titanate particles,
d. disrupting said agglomerates without substantially reducing the
size of the individual particles which comprised said agglomerates
to produce finely divided barium titanate powder having a mean
particle size below one micron.
19. The process of claim 17 wherein said barium and titanium
compounds are organic compounds.
20. The process of claim 17 wherein said barium compound is barium
acetate.
21. The process of claim 17 wherein said titanium compound is
triethanolamine titanate.
22. The process of claim 17 wherein said titanium compound is
tetraisopropyl titanate.
23. The process of claim 17 wherein said barium titanate also
contains other metal oxides.
24. A process for producing a sintered article comprised of a metal
oxide which is sinterable to essentially its theoretical density at
low temperatures, sid article having a compressive strength of at
least 5,000 pounds per square inch, which process comprises:
a. contacting a carbohydrate material with a compound of a metal to
form an intimate mixture thereof;
b. introducing said mixture into a heating zone having a
temperature sufficient to ignite said mixture but insufficient to
substantially sinter said metal compound;
c. igniting said mixture in said heating zone for a time period
sufficient to decompose and remove said carbohydrate material and
produce easily disrupted agglomerates of metal oxide particles of
sub-micron size,
d. disrupting sid agglomerates without substantially reducing the
size of the individual particles which comprised said agglomerates
to produce finely divided metal oxide powder having a mean particle
size of less than 0.1 micron,
e. shaping and compacting said powder into the form of said
article, and
f. sintering said shaped article at a temperature and for a period
of time sufficient to form said article.
25. A process for producing a sintered article comprised of
zirconia essentially at its theoretical density, said article
having a compressive strength of at least 5,000 pounds per square
inch, which process comprises:
a. contacting a carbohydrate material with a compound of zirconium
to form an intimate mixture thereof;
b. introducing said mixture into a heating zone having a
temperature sufficient to ignite said mixture but insufficient to
substantially sinter said zirconium compound;
c. igniting said mixture in said heating zone for a time period
sufficient to decompose and remove said carbohydrate material and
produce easily disrupted agglomerates of zirconia particles of
sub-micron size,
d. disrupting said agglomerates without substantially reducing the
size of the individual particles which comprised the agglomerates
to produce finely divided zirconia powder having a mean particle
size of less than 0.1 micron,
e. shaping and compacting said powder into the form of said
article, and
f. sintering said shaped article, at a temperature and for a period
of time sufficient to form said article.
26. A process for producing a sintered article comprised of thoria
essentially at its theoretical density, said article having a
compressive strength of at least 5,000 pounds per square inch,
which process comprises:
a. contacting a carbohydrate material with a compound of thorium to
form an intimate mixture thereof;
b. introducing said mixture into a heating zone having a
temperature sufficient to ignite said mixture but sufficient to
substantially sinter said thorium compound;
c. igniting said mixture in said heating zone for a time period
sufficient to decompose and remove said carbohydrate material and
produce easily disrupted agglomerates of thoria particles of
sub-micron size,
d. disrupting said agglomerates without substantially reducing the
size of the individual particles which comprised the agglomerates
to produce finely divided thoria powder having a mean particle size
of less than 0.1 micron,
e. shaping and compacting said powder into the form of said
article, and
f. sintering said shaped article, at a temperature and for a period
of time sufficient to form said article.
27. The sintered article comprised of thoria prepared by the
process of claim 26.
28. A process for producing a sintered article comprised of erbia
essentially at its theoretical density, said article having a
compressive strength of at least 5,000 pounds per square inch,
which process comprises:
a. contacting a carbohydrate material with a compound of erbium to
form an intimate mixture thereof;
b. introducing said mixture into a heating zone having a
temperature sufficient to ignite said mixture but insufficient to
substantially sinter said erbium compound;
c. igniting said mixture in said heating zone for a time period
sufficient to decompose and remove said carbohydrate material to
produce easily disrupted agglomerates of erbia particles of
sub-micron size,
d. disrupting said agglomerates without substantially reducing the
size of the individual particles which comprised the agglomerates
to produce finely divided erbia powder having a mean particle size
of less than 0.1 micron,
e. shaping and compacting said powder into the form of said
article, and
f. sintering said shaped article, at a temperature and for a period
of time sufficient to form said article.
29. A sintered article comprised of erbia prepared by the process
of claim 28.
30. A process for producing a sintered article comprised of two or
more metal oxides, said article having a surface area which is at
least 10 square meters per gram, and a compressive strength of at
least 5,000 pounds per square inch, which process comprises:
a. contacting a carbohydrate material with two or more compounds of
a metal to form an intimate mixture thereof;
b. introducing said mixture into a heating zone having a
temperature sufficient to ignite said mixture but insufficient to
substantially sinter said metal compounds;
c. igniting said mixture in said heating zone for a time period
sufficient to decompose and remove said carbohydrate material and
produce easily disrupted agglomerates of metal oxide particles of
sub-micron size, at least some of which metal oxide particles are
sinterable;
d. disrupting said agglomerates without substantially reducing the
size of the individual particles which comprised said agglomerates
to produce finely divided metal oxide powder having a mean particle
size of less than 0.1 micron,
e. shaping and compacting said powder into the form of said
article, and
f. sintering said shaped article, at a temperature and for a period
of time sufficient to form said article.
31. The process of claim 30 wherein said sintered article is
comprised of the oxides of zirconium and aluminum.
32. The process of claim 31 wherein said oxide of aluminum is
present in an amount of from about 5 to about 70 weight
percent.
33. The process of claim 30 wherein said sintered article is
comprised of the oxides of copper and aluminum.
34. The process of claim 33 wherein said oxide of aluminum is
present in an amount of from about 5 to about 70 weight
percent.
35. A sintered article comprised of the oxides of copper and
aluminum, said article being prepared by the process of claim
30.
36. The sintered article of claim 35 wherein aid oxide of aluminum
is present in an amount of from about 5 to about 70 weight percent.
Description
This invention relates to a process for the preparation of finely
divided metal oxides, to the metal oxide powders produced by the
process of the invention, and to high strength and/or high surface
area sintered metal oxide bodies prepared from them.
The prior art has disclosed various methods for producing
finely-divided metal oxides such as zirconia. For instance, one
method is disclosed by Mazdiyasni et al. in U.S. Pat. No. 3,432,314
and J. Am. Ceram. Soc., 50, page 532 (October 1967). This method
consists in precipitating zirconia from a solution of high purity
zirconium alkoxide. Simultaneously with the precipitation of
zirconia, a stabilizer oxide is also coprecipitated with the
zirconia. The finely-divided zirconia produced by Mazdiyasni et al.
by this co-precipitation technique is first dried, calcined, and
then crushed to a fine powder. The fine powder can be pressed to
produce a shaped body, which is then sintered at a temperature of
at least 1450.degree. C.
Other methods for making ultra-fine particle size zirconia include
the method known as the Sol-Gel process (R. G. Wymer et al, Proc
British Ceram. Soc., 7, 61, 1967), spray drying (B. Bovarnick et
al, U.S. Pat. No. 3,305,349), and freeze-drying (Schnettler et al.,
Sci. Ceram. 4, 79, 1967).
In the work reported by T. Vasilos et al in "Ultrafine-Grain
Ceramics, Proceedings of the 15th Sagamore Army Materials Research
Conference, August 1968", Syracuse University Press (1970), the
very fine particles that remained in suspension after repeated
centrifugation of Mazdiyasni et al. type zirconia powder were cast
into a disc having a green density of 72 percent of theoretical and
then sintered. Substantially fully dense zirconia was prepared at a
sintering temperature of only 1300.degree. C, however, the
specimens cracked during the experiment. Such a method for
producing ultra-fine particles would clearly be prohibitively
expensive since yields of the order of a fraction of one percent
would be expected.
Sintering temperatures of "1100.degree.-1500.degree. C" to product
zirconia of at least 90 percent of theoretical density are reported
for zirconia powder produced by a fluid energy mill (ref. --
British Pat. No. 1,177,596).
The present invention is based upon the discovery that ultra-fine
metal oxide powders can be prepared by a relatively uncomplicated
and inexpensive method. Many of the powders that are produced by
this method can be sintered essentially to their theoretical
densities at relatively low temperatures, that is, temperatures
significantly lower than those employed in the prior art. By the
process of this invention it is also possible to form intimate
mixtures of oxides and compounds without high temperature
treatment. The method of the invention comprises first contacting
one or more metal compounds with a carbohydrate material, igniting
the material to decompose and remove the carbohydrate material and
to insure conversion of substantially all of said metal compounds
to fragile agglomerates of its metal oxide, followed by
communication of the thus formed agglomerates to give the uniform,
ultra-fine powders of this invention.
By the term "metal oxide" as employed in the specification and
appended claims is meant a compound or compounds consisting of one
or more metals and oxygen. Examples of metal oxides which can be
prepared include such compounds as
1. TiO.sub.2
2. zirconia-yttria solid solution
3. Barium titanate
4. Mixtures of compounds or oxides such as zirconia-chromia.
By the term "comminution", "disruption" or "pulverizing" as used
throughout the specification and appended claims is meant the
separation of the individual particles which form the agglomerate
without the need for further subdivision or fracturing of the
particles. Hence any method which can achieve this end can be
employed. However, from a practical viewpoint it has been found
that wet ball milling accomplishes this best.
One of the advantages of this method is that the particles prepared
by this dispersive precursor method, and which make up the
agglomerate are already of the proper size and uniformity. Thus,
since the powders produced by this method have an extremely small
and uniform particle size, they can be sintered to form useful high
strength pressed bodies at relatively low sintering
temperatures.
A clearer understanding of the invention will be had by reference
to the accompanying drawings.
With reference to the drawings, FIGS. 1, 2 and 3 are sintering
curves of three different samples of pellets prepared from zirconia
powders. FIGS. 4, 5, 6 and 7 are pictures obtained by scanning
electron microscopy of commercially available zirconia powders and
zirconia powders prepared by the process of this invention.
FIG. 1 is a sintering curve obtained on an Orton Automatic
Recording Dilatometer of -325 mesh (U.S. Standard) yttria
stabilized zirconia powder supplied by the Zirconia Corporation of
America. The change in length, .DELTA.L/L, in arbitrary units is
plotted against temperature in degrees centigrade. As indicated in
Example 5, after compacting and sintering at the time and
temperature indicated, the pellets had a density of 3.9 grams per
cubic centimeter.
FIG. 2 is a sintering curve obtained on a yttria stabilized
zirconia powder prepared by the method of Mazdiyasni et al as set
forth in the above mentioned patent and which was supplied by the
HTM Company under the name Zyttrite. As indicated in Example 5,
after compacting and sintering, the final density of the pellets
was 5.3 grams per cubic centimeter.
FIG. 3 is a sintering curve of a yttria stabilized zirconia powder
prepared in accordance with Example 4 of this disclosure. As
indicated in Example 5, the pellet sintered to near its full
density, that is 5.9 - 6.0 grams per cubic centimeter.
From a comparison of FIGS. 1, 2 and 3 it is evident that the
commercial zirconia products never reached their full densities
even when the instrument achieved its highest temperature
(1450.degree. C). In contrast, sintered bodies prepared from the
powder of this invention approached their theoretical density
between 1200.degree. and 1300.degree. C. Hence it is evident that
the powders of this invention sintered at a much lower temperature
than the commercially available products.
FIG. 4 is a picture obtained by scanning electron microscopy (2200
magnification) of the -325 mesh zirconia powder as received from
the Zirconia Corporation of America. After compacting and sintering
at 1350.degree. C in accordance with the procedure of Example 5 the
sintered body had a density of 3.68 grams per square
centimeter.
FIG. 5 is a picture (2100 magnification) of the same zirconia as
shown in FIG. 4 but which had been subjected to wet ball milling.
After compacting and sintering at 1350.degree. C in accordance with
the procedure of Example 5 the sintered body had a density of 3.87
grams per cubic centimeter.
FIG. 6 is a picture (2400 magnification) of zirconia powder
prepared in accordance with the teachings of Example 1 of this
invention and dry ball milled. After compacting and sintering at
1350.degree. C the sintered body had a density of 4.36 grams per
centimeter.
FIG. 7 is a picture (2300 magnification) of the zirconia powder
shown in FIG. 6 which was re-milled under water. After compacting
and sintering at 1350.degree. C the sintered body had a density of
5.97 grams per cubic centimeter.
It is also evident from the electron microscope scans that the
commercially available zirconia, does not undergo significant
change in particle size even when wet ball milled and does not
sinter to near its theoretical density. In contrast the fragile
agglomerates prepared by the process of this invention (FIG. 6) are
readily broken up into ultra fine particles (FIG. 7) which do
sinter to near theoretical density.
As hereinbefore indicated the first step in the production of the
finely divided metal oxide powder is contacting the metal compound
with a carbohydrate material to form an intimate mixture thereof.
Impregnation procedures such as the precursor process disclosed in
U.S. Pat. No. 3,385,915 to B. H. Hamling can be used for the first
step. The disclosure of this patent is incorporated herein by
reference. Relatively inexpensive forms of carbohydrate material
can be used for this step of the invention. For instance, wood pulp
and cotton linters are useful inexpensive materials that can be
used for the impregnation, as well as the other types of materials
disclosed in said Hamling patent. Alternatively, a salt solution of
the element or elements of interest can be mixed with starch or a
solution of a soluble carbohydrate material such as glucose,
sucrose, or hydrolyzed starch. Hence the term "contacting" as
employed in the first step of the process of this invention is
intended to encompass both impregnation of solids materials and
dissolution in liquid materials to form intimate mixtures of the
two.
The metal salts employed in the first step are compounds of one or
more metals whose ashes will remain as agglomerates during the
ignition step, as opposed to densifying into solid coherent, large
particles which would then require fracturing during comminution
rather than disruption of the aggregates as employed in the instant
invention.
Examples of metals which can be employed in the process of this
invention to prepare single metal oxides are beryllium, magnesium,
calcium; the Group IIIB metals, i.e., scandium, yttrium and the
lanthanide and actinide elements; the Group IVB metals, i.e.,
titanium, zirconium, and hafnium; niobium and tantalum; the Group
VIB metals, i.e., chromium, molybdenum, and tungsten; manganese,
iron, cobalt, nickel, copper, zinc, cadmium, aluminum, gallium,
tin, lead and bismuth. The process of this invention can also be
employed to prepare metal oxides which are comprised of two or more
of the aforementioned metals.
In addition, it is possible to prepare metal oxides which contain
at least one of the above metals and one or more additional metals.
These oxides are stable and have melting points preferably above
700.degree. C. These include the Group IA elements with the
exception of hydrogen, (i.e., lithium, sodium, potassium, rubidium,
cesium), strontium, barium, germanium, vanadium, rhenium,
ruthenium, osmium, rhodium, indium, palladium, platinum, silver,
gold, mercury, iridium, thallium, and antimony.
It should be pointed out that the sintering rates of the different
metal oxides vary with the nature of the metal oxide. For example,
it has been found that although the sintering rate of alumina is
substantially increased when its powder is prepared according to
the process of this invention, it is still much less active to
sintering than zirconia powder.
Mixtures of such metal oxides with large differences in sintering
rates are particularly attractive for use in the formation of
sintered bodies having high surface area. In this particular case
the oxide which sinters rapidly acts as a ceramic glue to hold the
ultra-fine particles of the slower sintering component. A single
metal oxide such as zirconia typically has a low surface area, less
than 5 square meters per gram (m.sup.2 /g). However, when a
zirconia-alumina mixed oxide is made by the above described
precursor process, as indicated in Example 6, the resultant oxide
mixture has a different set of properties. The alumina particles
may be considered analogous to what ceramists refer to as a "grog".
Because of the small particle size of the precursor prepared, less
active alumina particles, the micro grog imparts high surface area
to the system, while the zirconia provides strength.
The concept of a micro grog is not limited to the zirconia-alumina
system, but encompasses other systems containing one or more easily
sintered oxides in conjunction with one or more less easily
sintered oxides. The criterion for easily sinterable and less
easily sinterable oxides can be determined from dilatometric traces
of the ultra-fine powders.
It has been observed that sintered articles prepared from mixed
metal oxide powders such as zirconia-alumina which have a mean
particle size below about 0.1 microns, are characterized by surface
areas of at least 10 meters per gram and compression strengths of
at least 5,000 pounds per square inch.
In practice, sintered zirconia-alumina articles having surface
areas as high as 50m.sup.2 /gm and higher, and compressive
strengths of at least 5,000 pounds per square inch are readily
obtained. Moreover, it has been observed that the surface area is
relatively stable over extended periods of time. For example,
sintered zirconia-alumina articles having surface areas in excess
of 50m.sup.2 /gm are stable for at least 150 hours at 950.degree.
C.
In general, it has also been observed that the component which is
less easily sinterable during the preparation of the metal oxide
article can be present in the article in an amount of from about 5
to about 70 weight percent. The particular range will, of course,
vary somewhat depending on the particular metal oxide being
prepared and the chemical properties of the two or more components
employed.
For some applications where high surface area is not important but
a relatively high strength is desired, the component which is less
easily sinterable during preparation of the metal oxide article can
be present in an amount of from about 70 to about 95 weight
percent.
The metal compounds that are employed in the impregnation step are
preferably water-soluble compounds such as halides, oxyhalides,
nitrates, sulfates, carboxylates, and the like. Specific
illustrative water soluble metal compounds include zirconyl
chloride, zirconium acetate, yttrium chloride, magnesium chloride,
thorium chloride, beryllium nitrate, calcium acetate, cupric
chloride, strontium nitrate, barium acetate, lanthanum nitrate,
aluminum chloride, titanium chloride, hafnium oxychloride, rare
earth metal acetates, rare earth metal chlorides, and the like.
The preparation of the oxides of barium from inorganic halides
requires that the halide ion be removed at some stage during the
process. Accordingly, in the preparation of the oxides of barium,
lanthanum, and other metals which form stable chloride salts, it is
preferred that a different inorganic salt or an organic compound be
employed as the starting material. Illustrative compounds include,
among others, nitrates, alkanoates, trialkanolamines, and the
like.
One preferred method of impregnation is to immerse the carbohydrate
material (preferably a cellulosic polymer such as wood pulp, cotton
or the like) in an aqueous solution of the metal compound(s). After
immersion the loaded material is removed from the solution and the
excess liquid is removed by centrifugation, squeezing, blotting, or
the like. Centrifugation is a preferred method for removal of the
excess liquid.
With liquid precursor compositions, e.g. solutions containing
soluble carbohydrates, the preferred method is to dehydrate and
char the mixture by heating. During the first stages of charring,
the solution becomes progressively darker but stays clear while
voluminous bubbles form. As the charring process continues, the
solution turns black and very viscous until the solution is
transformed into a voluminous solid char.
Although solution charring is a suitable and much recommended
method of preparing the material for ignition, other methods of
drying, charring and igniting the preparations would be
satisfactory as well. Examples of such methods would spray drying
or thin film drying following by ignition, or even direct ignition
of the solution in such a way that drying, charring and igniting
would be obtained in a single operation.
The second step in the production of the finely divided metal oxide
is the ignition of the carbohydrate material containing the metal
compound inpregnated therein. The ignition can be carried out
simply by rapidly heating the loaded material in air to a
temperature sufficient to ignite the carbohydrate material.
In many cases, the term "ignition" implies combustion accompanied
by flame. However, flame is not necessarily present in all cases of
ignition as desired in the present invention. The important factor
is to effect decomposition and removal of the carbohydrate material
by a method which produces fragile agglomerates of very small
particles of metal compound(s) which are present in the interstices
of the decomposing carbohydrate.
Thus, during the ignition step of this invention the temperature
preferably should not reach the temperature at which sintering to
uniform relatively non-fragile agglomerates occurs. This
temperature varies from one metal oxide to another, but will
normally be from about 900.degree. C to about 1300.degree. C. For
zirconia, for example, it is desired not to exceed about
1000.degree. C to about 1100.degree. C. In some instances,
temperature as low as 700.degree. C or less should be employed.
The foregoing rather lengthy discussion of the ignition step should
not be allowed to obscure the fact that the ingnition step can be
carried as a very uncomplicated operation. For example, the
ingition can be carried out by first drying the metal compound
loaded material by any convenient method, followed by inserting the
dried, loaded material in an oven maintained at a temperature of
from about 300.degree. C to about 900.degree. C, and preferably
from about 400.degree. C to about 800.degree. C. Ignition is
continued until essentially all of the carbohydrate material has
been removed. The time is not critical, for instance, ignition
times of from about 0.5 to about 5 hours are typical.
The preparation of barium titanate powders from organo-titanium
compounds offers several advantages. Of principal importance it
yields barium titanate directly by ignition without the presence of
any unwanted phases. The barium titanate produced is a single
phase, chemically pure, and consists of very fine crystallites of
high surface area and in a state of extremely fine dispersion. This
process is simple, flexible in its operation, does not require any
overly specialized equipment and is devoid of any difficult and
time consuming operations. Although there is a lower limit in the
amount of carbohydrate to be used, slight departures do not
adversely affect the product. The workable range of carbohydrate
concentration is wide since its upper limit is dictated more by the
economics rather than by the chemistry of the process. The process
is a pyrolytic process and the barium titanate powder is produced
directly as a dry powder, ready for use, without the necessity for
filtering and drying. The process is also flexible in terms of
stoichiometry. Slight deviations from the purely stoichiometric
compound are often preferred. They can easily be obtained by small
compositional variations in the starting solutions without
affecting the process.
When producing powdered zirconia, in many cases it is preferred to
produce the zirconia powder in a stabilized form. Therefore, a
compound of yttrium, calcium, magnesium, rare earth metal or other
knon metals that form a stabilizer oxide can be employed along with
the zirconium containing compound in producing the loaded material.
The proportions of the zirconium compound and stabilizer metal
compound should be selected to produce the type of stabilized
zirconia desired.
After ignition, the metal oxide (which can be referred to at this
point as an "ash") is comminuted to break up the fragile
agglomerates to form the ultrafine powder of the invention. The
comminution can be effected by any convenient method which is
suitable for this purpose. Wet ball milling, is preferred although
other methods for producing ultra-fine particles can be employed,
if desired. It is important to note that if the process of this
invention is not employed, it is very difficult to grind most solid
materials to sizes finer than about 4 microns. The problems
associated with grinding to small sizes are well known to those
skilled in this art, and these problems have been described in
detail in the literature, as, for example, in the chapter on Size
Reduction by Clyde Orr, Jr. in the Kirk-Othmer "Encyclopedia of
Chemical Technology", 2nd Edition, Volume 18, pages 340;
358-60.
Usually, special equipment such as fluid energy mills or colloid
mills, rather than ball-mills, are needed to achieve the micron or
submicron range. Even with the special equipment, obtaining
submicron size is difficult. Thus, an essential feature of this
invention is that incorporating an inorganic material or
organometallic into a carbohydrate matrix, followed by ignition
gives rise to aggregates that can be reduced to submicron sizes by
conventional means. This was an unexpected result, and is distinct
from the findings of B. H. Hamling as set forth in U.S. Pat. No.
3,385,915. Hamling's earlier work was directed toward the
preparation of high strength fibers. Failure to follow the
recommended procedure as, for example, the experiment referred to
in column 15, lines 5-8 in his patent was expected to yield a
material with normal size reduction properties, not a material for
which size reduction was unusually easy.
The present drawings clearly show the difference between a material
of normal size reduction properties and materials prepared by the
process of this invention. For example, FIGS. 4 and 5 show a
conventional material before and after ball-milling. There was
little size reduction. FIGS. 6 and 7 are for a material prepared
according to the method of this invention. FIG. 6 shows
agglomerates, and FIG. 7, the same material after ball-milling. It
is evident that the aggregates of FIG. 6 were broken up, but those
of FIG. 4 were not. Thus, there is a clear distinction between
easily disrupted aggregates and conventional particles.
The actual carrying out of the comminution step is not narrowly
critical, however as indicated in the paragraph above, wet ball
milling is preferred. The comminution is continued for a period of
time sufficient to disrupt the fragile agglomerates into ultra-fine
particles. To illustrate the physical operation involved in the
comminution step, laboratory scale batches of zirconia ash have
been wet ball milled (using a laboratory scale mill and 1-2
millimiter zirconia beads as the balls) to the desired ultra-fine
particle size in from 4 to 8 hours. This is given merely as an
illustration of one mode of carrying out the invention. When wet
ball milling, it is sometimes necessary to use a non-aqueous media
if the particular metal oxide undergoes hydrolysis, as is the case
with alumina, magnesia, and others. Different comminution times can
be encountered with other metal oxides and/or with other
comminution equipment. The point to be emphasized is that metal
oxides prepared by ignition of loaded carbohydrate polymers can be
comminuted by conventional means to the desired ultra-fine particle
size powders, whereas metal oxides prepared by other methods, such
as the Hamling method, apparently cannot (at least, not with any
practicable expenditure of energy).
It is sometimes advantageous to employ a particle size separation
procedure after wet ball milling to separate particles that are
liberated during the de-agglomeration step from aggregates that are
only partially disrupted. This can be done conveniently by
treatment such as those described in U.S. Pat. Nos. 2,661,287;
3,297,516 and 3,409,499 which enhance the surface charge of
particles therefore permitting the formation of a colloidal
dispersion. The particles prepared by the procedure of this
invention are so small that settling rates are extremely slow, thus
aggregates which have not been completely disrupted during wet ball
milling can be separated from dispersed suspensions of liberated
particles by sedimentation, centrifugation, or other separation
procedures based on particle size or mass. Once the separation has
been made, the liberated particles remaining in suspension can be
conveniently collected by treatments that reduce the surface charge
and render the colloidal suspension unstable. Typical treatments
are the addition of a base to raise the pH of the suspension, or
the addition of a salt having a multivalent anion. The suspensions
treated in this manner revert to a flocculated condition, and in
this form, the powder can be separated from the bulk of the
suspending medium by filtration or sedimentation.
It has been observed that the mean particle size is below 1.0
micron, and usually below 0.1 micron. The individual particles
remain unresolved at 11,000 magnification. X-ray powder diffraction
analysis indicates an ultimate particle size within the range of
from about 200 to about 1000 Angstroms.
One way to characterize the powder is in terms of its sinterability
at temperatures substantially lower than the temperatures that have
been employed with metal oxide powders heretofore available. With
zirconia, for instance, after the powder has been compacted to
about 40 percent of fully dense zirconia, the compacted zirconia
sinters, without application of external pressure (and without the
use of sintering aids), to a shape having a density of at least 90
percent of fully dense zirconia at a temperature of from about
1100.degree. to about 1200.degree. C.
The invention also provides sintered metal oxide bodies having
strengths significantly higher than sintered metal oxide bodies
heretofore available. The high strength of thse sintered bodies is
apparently the direct result of the ability of the finely divided
metal oxide powders of the invention to sinter at substantially
lower temperatures than the prior art metal oxide powders. Because
of the lower sintering temperatures, grain growth is lessened.
Since strength, in many cases, bears an inverse relationship to
grain size, the smaller grain size of the sintered metal oxides of
the invention yields sintered bodies of higher strength. For
example, sintered zirconia articles have been prepared having
essentially the theoretical density of zirconia and modulus of
rupture of greater than about 100,000 pounds per square inch.
The sintered metal oxide objects of the invention can be prepared
by conventional sintering techniques, except that the temperatures
that can be employed are significantly lower than those heretofore
employed for sintering metal oxide powders. The metal oxide powders
can be hot pressed, or they can be cold pressed followed by heating
to sintering temperature.
The finely divided metal oxides of the invention comprise a class
of known materials in a novel form, i.e. having ultra-fine particle
size. The known utility (e.g. as polishing powders and as additives
such as opacifiers for glass) of these metal oxides is enhanced, in
many cases, by the ultra-fine particle size provided by the
invention. The finely divided metal oxides of the invention can
also be employed in the preparation of heat shields, and the like,
by the fabrication technique described in U.S. Pat. No. 3,736,160
by B. H. Hamling entitled "Fibrous Zirconia/Cement Composities",
issued May 29, 1973. The metal oxide powders, particularly mixed
metal oxide powders, are useful in the preparation of high strength
compacted shapes which can be utilized in high temperature, and/or
corrosive environments. High strength and high surface area
sintered bodies can be utilized in the preparation of catalysts,
catalyst supports an the like. The sintered metal oxide objects of
the invention can also be used as refractories, crucible liners,
heat shields, and the like.
The present invention is particularly attractive for the
preparation of highly reactive, high surface area, powders, which
are useful in commercial dielectric formulations. These
formulations consists of at least two and in some cases more than
four simple and mixed-cation oxides including barium titanate. As
previously indicated the mixed oxides powders are obtained by
contacting the cation precursors with an aqueous carbohydrate
solution followed by drying, charring, and igniting. The powders
can be sintered to dense bodies at lower final firing temperatures
and the sintered bodies have values of dielectric constant and
temperature coefficient of dielectric constant unlike those of
conventional dielectrics of the same analysis.
The dielectric formulations containing the sintered powders of this
invention are the subject matter of application Ser. No. 536,620,
entitled "High Dielectric Constant Ceramic Body made from Fine
Particle Ceramic Powders", filed Dec. 26, 1974, by R. C. F. Hanold
III, and assigned to the same assignee as this invention.
The following examples illustrate the invention:
EXAMPLE 1
A typical method of producing yttria-stabilized zirconia powder is
the following:
1. Contact sheets of wood pulp, by immersion, in an aqueous
solution of zirconium oxy-chloride and yttrium chloride, having a
specific gravity of 1.35 and containing 250 gm/liter ZrO.sub.2, 20
gm/liter mixed Y.sub.2 O.sub.3 and rare earth oxide and 160
gm/liter chloride ion.
2. After thorough saturation of the solution into the wood pulp,
(time may vary from several minutes to a day or more) the pulp is
squeezed or centrifuged to remove excess solution, i.e., solution
not absorbed into the pulp.
3. The wet, salt-loaded pulp is next ignited in a commercial
gas-fired incinerator. During burning the matrial reaches a maximum
temperature of around 1800.degree. F for several minutes.
4. After the charge has completely burned, the white ash is
collected. The ash at this point is a soft, fluffy material
composed of loosely agglomerated crystallites of stabilized
zirconia. Particle sizes of the crystallites, as determined by
X-ray diffraction line broadening analysis and electron microscopy,
are in the 200-500 Angstrom range. The ash is next broken down to
about 100 mesh size in a blender or pulverizer and then wet milled
for 4 to 8 hours. Zirconia beads have been used as the grinding
media in small preparations, but other hard grinding media are
acceptable.
EXAMPLE 2
Ten pounds of paper grade wood pulp (Rayonier Bleached Sulfite No.
2) was soaked in 5 gal. zirconium oxychloride and yttrium chloride
solution for a period of 10-15 minutes. The solution was at room
temperature and had the following composition:
ZrO.sub.2 -- 250 gm/liter
Y.sub.2 o.sub.3 -- 16 gm/liter
C1.sup.- -- 163 gm/liter
Sp. Gr. -- 1.350
The excess (non-impregnated) solution was removed by passing the
wood pulp (in the form of sheets) through pressure rolls at 2 Tons
nip pressure. After rolling, the wet pulp weighed 18.0 lbs. The
pulp while still wet was placed in a commercial incinerator and
ignited to ashes. A period of 4-6 hours was required to completely
burn the wet pulp to ash. The white, fluffy ash weighing 2.1 lb.
was collectd from the incinerator and placed in an electrically
heated furnace (Blue M Electric Co.) and raised to 1830.degree. F
for a period of 3 hrs.
Next, the ash was wet milled for a period of 8 hrs. A one-gal.
rubber lined ball mill was used. Milling media was zirconia beads
(ZIRCOA No. 1304, -10 +20 Mesh). The milled powder was wet screened
through 400 mesh screen, allowed to settle, decanted and dried at
240.degree. F.
EXAMPLE 3
A 1.0 gram portion of the zirconia powder of Example 2 was
fashioned into rectangular pellets with initial dimensions of
approximately 3/4 .times. 1/4 .times. 1/8 inches. Two such pellets
were cold-pressed at approximately 18,000 psi, and sintered at
1300.degree. C for 17 hours. After sintering, the surfaces of the
pellets were polished with 600 grit diamond. Room temperature
modulus of rupture values on these pellets, as determined by the
three point bend test over a one-half inch span, were 134,000 and
129,000 psi. This is a 5- to 10- fold increase over the modulus of
rupture values encountered for most conventional ceramic
specimens.
EXAMPLE 4
An approximate 1 gram portion of yttria-stabilized zirconia powder
prepared by a procedure analogous to that described in Example 2
was fashioned into a cylindrical pellet by pressing at 50,000 psi
at room temperature in a steel die. A 0.5% solution of stearic acid
in acetone was used as a die lubricant. The pellet was then
sintered by heating in air to 1350.degree. C over a period of
approximately 20 minutes, and holding temperature for 1 hour.
______________________________________ apparent diameter thickness
density ______________________________________ After cold pressing
1.29 cm 0.30 cm 2.6, g/cm.sup.3 After sintering 0.97 0.23 6.0
______________________________________
EXAMPLE 5
Sheets of paper pulp were impregnated with a zirconyl chloride -
yttrium chloride solution as described in Example 1. The excess
solution was removed by centrifuging for 10 minutes at 4000 rpm in
a 11 inch diameter basket. The wet, salt-loaded pulp was then
ignited in a muffle furnace maintained at 600.degree. C. The
resultant ash was ball-milled under water using 1-2 mm diameter
zirconia beads. Following ball-milling, the suspension was diluted
to 3 liters and acidified was 20 ml of 1 molar acetic acid. 300 ml
portions of the acidified suspension were sheared for 5 minutes in
a Waring Blendor, then centrifuged for 15 minutes at 2000 rpm (mean
suspension diameter, 16 inches). The material remaining in
suspension was separated from the settled solids by decantation,
and collected by raising the pH of the suspension to approx. pH 10
with ammonium hydroxide so as to induce flocculation. The
flocculated powder was collected by centrifugation at approx. 500
rpm, and was reslurred and resettled three times in acetone so as
to facilitate drying. The acetone and residual water were removed
by drying in air at approx. 100.degree. C and the yttria-stabilized
zirconia powder recovered.
Pellets were prepared in the manner described in Example 4, of (a)
the yttria-stabilized zirconia powder prepared by this example, (b)
a yttria-stabilized zirconia powder prepared by the method of
Mazolyasni, et al. which was supplied by the HTM Company under the
name Zyttrite, (c) a -325 mesh yttria-stabilized zirconia powder
supplied by the Zirconium Corporation of America. The pellets were
sintered by heating from room temperature to 1465.degree. C at a
heating rate of 3.3.degree. C/min. After cooling to room
temperature at approximately the same rate, the final densities
were as follows:
______________________________________ Powder Density, g/cm.sup.3
______________________________________ Powder prepared by 5.9-6.0
this Example. Zyttrite 5.3 -325 mesh powder 3.9
______________________________________
EXAMPLE 6
A solution containing zirconyl chloride and aluminum chloride each
in an amount equivalent to 50 grams per liter of the respective
oxides was mixed with an equal volume of Karo light corn syrup. The
mixture was dried and charred by heating overnight at approx.
90.degree. C. The resultant char was ground to -10 mesh and ignited
in a muffle furnace that was maintained at 400.degree. C. The char
was ignited in increments by adding a layer consisting of 250 to
300 ml of char to a 6 .times. 12 inch tray about every 30 minutes.
When the char addition was complete, the resultant char was held at
400.degree. C overnight. Ball-milling, size separation, and drying
was carried out in a manner analogous to that described in Example
5.
Six cylindrical pellets 3/8 inch in diameter and 1/4 inch high were
prepared from this powder and heated to 900.degree. C in 45 minutes
and held 2 hours. Two pellets were removed and the temperature was
increased to 1000.degree. C and maintained for 2 hours. Two more
pellets were removed and the temperature was raised to 1100.degree.
C and maintained for two hours. Property data on the pellets were
as follows:
______________________________________ Average Average Nitrogen BET
Temp. Density Compression Strength Surface Area
______________________________________ 900.degree. C 1.58
g/cm.sup.3 10,400 psi 87 m.sup.2 /g 1000 1.79 10,100 psi 48 m.sup.2
/g 1100 1.91 10,000 psi 21 m.sup.2 /g
______________________________________
EXAMPLE 7
Zirconia-alumina tow was prepared by the relic process as disclosed
in Belgian Pat. No. 746,113. A sample of the tow was ground dry in
a Mini-Blendor, and compacted into pellets in a manner similar to
that described in Example 6. The pellets were heated to
1100.degree. C at the same rate indicated in Example 6. The results
obtained were as follows:
______________________________________ Compressive Nitrogen BET
Temperature .degree. C. Density Strength Surface Area
______________________________________ 900 1.66 1,060 psi 98 1000
1.92 1,220 psi 52 1100 2.35 1,450 psi 3
______________________________________
EXAMPLE 8
A solution contaning 1.8 moles per liter cupric chloride and 1.5
moles per liter aluminum chloride was mixed with an equal volume of
Karo light corn syrup. The mixture was dried and charred by heating
in air at approx. 90.degree. C overnight, then ignited in a muffle
furnace that was maintained at 400.degree. C. The resultant ash was
heated further at 800.degree. C for 2 hrs., then ball-milled under
water using 1 to 2 mm diameter zirconia beads. The resultant powder
was collected by centrifugation, rinsed with acetone to facilitate
drying, and dried in a vacuum chamber maintained at 40.degree.
C.
Cylindrical pellets of this powder were pressed at 2000 lb. force
on a three-eighth inch diameter die. When heated from room
temperature to 1000.degree. C at 3.degree. C/min., the pellets had
an average density of 2.24 g/cm.sup.3, an average crush strength of
16,700 psi, and a surface area of 15.3 m.sup.2 /g. X-ray
diffraction showed lines characteristic of CuO (ASTM Card 5-0661)
and CuO . Al.sub.2 O.sub.3 (ASTM Card 2-1414).
EXAMPLE 9
Paper pulp was impregnated with an erbium chloride solution
containing the equivalent of 360g Er.sub.2 O.sub.3 /l. The salt
loaded pulp was centrifuged and ignited as described in Example 5,
then heated further at 800.degree. C for 1.5 hrs. The powder was
then ball-milled under methanol using 1- 2 mm diameter zirconia
beads. After drying in vacuum at 40.degree. C, a cylindrical pellet
of the powder sintered to a density of 8.3 g/cm.sup.3 when heated
to 1465.degree. C at 3.3.degree. C/min.
EXAMPLE 10
A spinel powder was prepared by impregnating paper pulp with a
solution containing the equivalent of 100 g Al.sub.2 O.sub.3 per
liter and 40 g MgO per liter. The salt-loaded pulp was processed in
a manner analogous to that described in Example 5, except the ash
resulting from ignition was heated further at 800.degree. for 1.5
hrs., and the final powder was dried in vacuum at 40.degree. C
instead of in air at 100.degree. C. A cylindrical pellet of this
material sintered to a density of 3.4 g/cm.sup.3 when heated to
1465.degree. C at 3.3.degree. C/min.
EXAMPLE 11
Using the procedure described above for spinel, a thoria powder was
prepared starting with a thorium nitrate solution containing the
equivalent of 527 g ThO.sub.2 /l. A cylindrical pellet of this
material sintered to a density of 9.8 g/cm.sup.3 when heated to
1465.degree. C at 3.3.degree. C/min.
EXAMPLE 12
In a manner similar to that employed in the previous examples a
mixture of 127 milliliters of ZrOCl.sub.2 (342 grams ZrO.sub.2
/liter), 100 milliliters of CrCl.sub.3.6H.sub.2 O (1 lb./liter)
41.4 milliliters CuCl.sub.2.2H.sub.2 O (1 lb/liter) and 1 pint of
Karo syrup was dehydrated on a hot plate, further dried at
95.degree. C. for approximately 1 hour ans ignited at 600.degree. C
in air. The powder, ZrO.sub.2 -Cr.sub.2 O.sub.3 -CuO, was hand
ground, rinsed with water, and dried at 100.degree. C over the
weekend. The powder was ground to 100 mesh, formed into a pellet at
6000 lb. force using a 2 inch diameter die. The pellet was then
ground to 10/20 mesh.
EXAMPLE 12
The purpose of this example was to demonstrate the preparation of
sub-micron size barium titanate powder. The solution used in this
example was prepared in the following way: an aqueous solution of
tetraisopropyl titanate was first prepared by slowly adding 100 g
of tetraisopropyl titanate to 200g of glacial acetic acid with
agitation. The whole solution was then added slowly to 700 g of
water with agitation. The aqueous solution of tetraisopropyl
titanate so prepared was then added to and thoroughly mixed with
about one liter of corn syrup (Globe), 89.4g of anhydrous barium
acetate were then separately dissolved in enough water to obtain
complete dissolution. The barium acetate solution was then added to
and thoroughly mixed with the tetraisopropyl titanate corn syrup
solution. The resulting solution was then heated on a hot plate
until dry. During this process, the solution was converted into a
char. The resulting char was then ignited in a furnace at
600.degree. C with an excess of air until all the carbonaceous
material was burned off. The resulting powder was characterized by
x-ray diffraction to be barium titanate. Its crystallite size was
estimated from x-ray line broadening to be in the 510 A range.
EXAMPLE 14
The purpose of this example was to demonstrate the preparation of
sub-micron size barium titanate powder. The solution used in this
example was prepared in the following way: 22.22g of anhydrous
barium acetate were dissolved into 50cc of water, 213.5g of corn
syrup (Isomerose) were added to and thoroughly mixed with that
solution, 50g of 80 wt.% triethanolamine titanate in isopropanol
was then added to and thoroughly mixed with the brium acetate -
corn syrup solution. In the same manner as in Example 13 the
resulting solution was converted to a char, which was then ignited
at 600.degree. C in air. The resulting powder was characterized by
x-ray diffraction to be barium titanate. Specific surface area of
the powder was measured by B.E.T. to equal 17 m.sup.2 /g.
Crystallite size of the powder was estimated from x-ray line
broadening to be in the 310 A range.
EXAMPLE 15
The purpose of this example was to demonstrate the preparation of
sub-micron size barium titanate powder. The solution used in this
example was prepared in the following way: 100g of reagent grade
sucrose was dissolved in 150 cc of warm water, 22.22 g. of
anhydrous barium acetate was added and dissolved into the sucrose
solution, 50g of 80 wt.% triethanolamine titanate in isopropanol
were then added to and thoroughly mixed with the barium
acetate-sucrose solution. In the same manner as in example 13, the
resulting solution was converted to a char, the char was then
ignited at 600.degree. C in air. The resulting powder was
characterized by x-ray diffraction to be barium titanate. Specific
surface area of the powder was measured by B.E.T. to equal 17.2
m.sup.2 /g. Crystallite size of the powder was estimated from x-ray
line broadening to be in the 360 A range.
EXAMPLE 16
The purpose of this example was to find out whether the
carbohydrate material was necessary in the preparation of barium
titanate by the method described above. The solution used in this
example was prepared in the following way: 464.6g of anhydrous
barium acetate was dissolved in enough water to obtain complete
dissolution. The barium acetate solution was then added to and
thoroughly mixed with 1 liter of 80 wt.% triethanolamine titanate
in isopropanol. Upon adddition of the barium acetate solution a
small amount of precipitate formed. In the same manner as in
Example 13, the resulting mixture was heated on a hot plate until
dry. During this process a gelatinous precipitate formed prior to
the formation of the char. The resulting char was then ignited at
600.degree. C in air. The resulting powder was characterized by
x-ray diffraction to be a mixture of barium carbonate and titanium
oxide.
EXAMPLE 17
The purpose of this example was to demonstrate the preparation of
sub-micron size barium titanate powder containing 10% by weight
calcium zirconate. The solution used in this example was prepared
in the following way: 500g of commercial surcrose was dissolved
into 750cc of warm water, 111.5g of anhydrous barium acetate was
added and dissolved into the sucrose solution, 250g of 80wt.%
triethanolamine titanate in isopropanol were then added to and
thoroughly mixed with the resulting solution, 41.1cc of an aqueous
solution of calcium acetate (containing 3.49g CaO) previously
prepared by dissolving 955g of anhydrous calcium acetate in enough
water to yield 4 liters of solution and assayed to contain 84.5g of
CaO per liter of solution, were added to and thoroughly mixed with
the sucrose solution; 21cc of aqueous zirconium acetate solution
(containing 7.57g of ZrO.sub.2) was added and thoroughly mixed with
the sucrose solution. In the same manner as in Example 13, the
resulting aqueous mixture was converted to a char. The char was
then ignited at 600.degree. C. The resulting powder was
characterized by x-ray diffraction to be barium titanate with
calcium zirconate in solid solution. Specific surface area of the
powder was measured to equal 20.85 m.sup.2 /g. Crystallite size of
the powder was estimated from x-ray line broadening to be in the
235 A range.
EXAMPLE 18
The purpose of this example was to demonstrate the preparation of
sub-micron size bariium titanate powder containing 13 wt.% bismuth
titanate. The solution used in this example was prepared in the
following way: 600g of commercial sucrose was dissolved in 800cc of
warm water, 111.5g of anhydrous barium acetate was added to and
dissolved into that solution, 278.4g of 80 wt.% triethanolamine
titanate in isopropanol was then added to and thoroughly mixed with
the sucrose solution, 48.2g of bismuth ammonium citrate solution,
containing 11.55g of Bi.sub.2 O.sub.3, was added to the sucrose
solution. Upon addition of the bismuth ammonium citrate solution, a
gelatinous precipitate formed which was dissolved by heating the
mixture to 74.degree. C. In the same manner as in Example 13, the
resulting solution was converted to a char. The char was then
ignited at 600.degree. C in air. The resulting powder was
characterized by x-ray diffraction to be barium titanate with
bismuth titanate in solid solution. Specific surface area of the
powder was measured to equual 18.8 m.sup.2 /g. Crystallite size of
the powder was estimated from x-ray line broadening to be in the
270 A range.
EXAMPLE 19
The purpose of this example was to demonstrate the prepartion of
sub-micron size barium titanate powder containing 9 wt.% of calcium
stannate. The solution used in this example was prepared in the
following way: 600g of commercial sucrose was dissolved into 750cc
of warm water, 111.5g of anhydrous barium acetate was added to and
dissolved into that solution, 250g of 80 wt.% triethanolamine
titanate in ispropanol was then added to and thoroughly mixed with
the sucrose solution, 32.6cc of calcium acetate solution,
containing 2.77g of CaO, as used in Example 17, was then added to
and thoroughly mixed with the sucrose solution, 350cc of glacial
acetic acid containing 6.645g SnO in solution, was then added to
and thoroughly mixed with the sucrose solution. In the same manner
as in Example 13, the resulting mixture was converted to a char.
The char was then ignited at 600.degree. C in air. The resulting
powder was characterized by x-ray diffraction to be barium titanate
with calcium stannate in solid solution. Specific surface area of
the powder was measured to equal 22.95 m.sup.2 /g. Crystallite size
of the powder was estimated from x-ray line broadening to be in the
250 A range.
EXAMPLE 20
the purpose of this example was to demonstrate the preparation of
sub-micron size barium titanate powder containing 11.9 wt.% bismuth
titanate, 7.9 wt.% calcium stannate, 0.8 wt.% cobalt oxide and 0.2
wt.% manganese oxide. The solution used in this example was
prepared in the following way: 600g of commercial sucrose was
dissolved into 750cc of warm water 111.5g of anhydrous barium
acetate was added to and dissolved into that solution, 0.325cc of
manganous nitrate 50 wt.% solution was added to and thoroughly
mixed with the sucrose solution, 278.4g of 80 wt.% triethanolamine
titanate in isopropanol was then added to and thoroughly mixed with
the sucrose solution, 0.86g of hydrous cobalt acetate was added to
and dissolved in the sucrose solution, 48.2g of bismuth ammonium
citrate solution, containing 11.55g of Bi.sub.2 O.sub.3, was added
to and thoroughly mixed to the solution in the same way as
described in Example 18, 30.9cc of calcium acetate solution
containing 2.62g of CaO, as used in Example 17 was added to and
thoroughly mixed with the sucrose solution, 500cc of glacial acetic
acid containing 5.825g Sn in solution, was then added to and
thoroughly mixed with the solution. In the same manner as in
Example 13 the resulting solution was converted to a char. The char
was then ignited at 600.degree. C in air. The resulting powder was
characterized by x-ray diffraction to be barium titanate with the
oxide additives in solid solution. Specific surface area of the
powder was measured to equal 19.87 m.sup.2 /g. Crystallite size of
the powder was estimated from x-ray line broadening to be in the
250 A range.
EXAMPLE 21
The purpose of this example was to demonstrate the preparation of
sub-micron size barium titanate powder containing 2.5% by weight
sodium bismuth titanate (NaBi.sub.9 Ti.sub.8 O.sub.30). The
solution used in this example was prepred in the following way:
500g of commercial sucrose was dissolved into 500cc of warm water,
104g of anhydrous barium acetate was added and dissolved into the
sucrose solution, 238.26g of 80 wt.% triethanolamine titanate in
isopropanol were then added to and thoroughly mixed with the
resulting solution, 0.148g of anhydrous sodium acetate was added to
and dissolved in the sucrose solution, 15.81g of bismuth ammonium
citrate solution, containing 3.788g of Bi.sub.2 O.sub.3, was added
to and thoroughly mixed with the solution. Upon addition of the
bismuth ammonium citrate solution, a gelatinous precipitate formed
which was dissolved by heating the mixture to 74.degree. C. The
resulting solution was converted to a char by heating, and the char
was then ignited at 600.degree. C in air. The resulting powder was
characterized by X-ray diffraction to be barium titanate with the
oxide additions in solid solution. Specific surface area of the
powder was measured to equal 13.04 m.sup.2 /g. Crystallite size of
the powder was estimated from X-ray line broadening to be in the
450 A range.
EXAMPLE 22
The purpose of this example was to demonstrate the preparation of
sub-micron size barium titanate powder containing 1 wt.% of
chromium oxide. The solution used in this example was prepared in
the following way: 220g of anhydrous barium acetate was dissolved
into one liter of water, 1500g of corn syrup was added to and
thoroughly mixed with the barium acetate solution, 500g of 80 wt.%
triethanolamine titanate in isopropanol was then added to and
thoroughly mixed with the resulting solution; the resulting
solution was then divided into two equal parts and 3.25g of
chromium acetate was added to and dissolved into one of the equal
parts. The resulting solution was converted to a char by heating
and the char was then ignited at 600.degree. C in air. The
resulting powder was characterized by X-ray diffraction to be
barium titanate doped with chromium oxide. Specific surface area of
the powder was measured to equual 7.72 m.sup.2 /g. Crystallite size
of the powder was estimated from X-ray line broadening to be in the
600 A range.
EXAMPLE 23
The purpose of this example was to demonstrate the preparation of
sub-micron size calcium zirconate powder. The solution used in this
example was prepared in the following way: a solution of calcium
acetate was first prepared by dissolving approximately 955g of
monohydrated calcium acetate in enough water to yield approximately
4 liters of solution which was assayed to contain the equivalent of
84.85 g of CaO per liter; 661 cc of the calcium acetate solution
containing 56 g of CaO and 338 cc of commercial zirconium acetate
solution assayed to contain the equivalent of 364.6g of ZrO.sub.2
per liter and containing the equivalent of 123.25g of ZrO.sub.2
were added and thoroughly mixed with one liter of corn syrup. The
resulting solution was converted to a char by heating and the char
was then ignited at 650.degree. C in air. The resulting powder was
characterized by X-ray diffraction to be calcium zirconate with a
small amount of zirconia and calcia as separate phases. Specific
surface area of the powder was measured to equal 14.5 m.sup.2
/g.
EXAMPLE 24
The purpose of this example was to demonstrate the preparation of
sub-micron size potassium tantalate niobate powder. The solution
used in this example was prepared in the following way: 50cc of
tantalum oxalate solution, containing the equivalent of 0.023 mole
tantalum pentoxide, 75cc of niobium oxalate solution containing the
equivalent of 0.023 mole niobium pentoxide and 6.35g of potassium
carbonate corresponding to 0.046 mole of potassium oxide were mixed
together with 200cc of corn syrup. Upon mixing, a precipitate
formed which was dissolved by addition of oxalic acid. The
resulting solution was converted to a char by heating and the char
was then ignited at 600.degree. C in air. The resulting powder was
characterized by X-ray diffraction to be potassium
tantalate-niobate solid solution, having the perovskite structure.
Specific surface area of the powder was measured to equal 8.25
m.sup.2 /g.
EXAMPLE 25
In a similar manner to that employed in the previous examples, a
series of experiments were conducted to illustrate the preparation
of other metal oxides. In all cases, a water soluble cation salt
was dissolved in a solution containing 4 or more grams of sugar per
gram of anticipated oxide yield and the solution was dried,
charred, and ignited. The results of this series are summarized in
Table I.
TABLE I ______________________________________ Ignition Surface
Oxide Starting Solution Temp. Area
______________________________________ 1 CdO Cadmium Acetate, Sugar
400.degree. C 3 m.sup.2 /g 2 CdO Cadmium Acetate, EDTA* 400.degree.
C 2.9 m.sup.2 /g (complexing agent), Sugar 3 Bi.sub.2 O.sub.3
Bismuth Ammonium Citrate 475.degree. C 1.0 m.sup.2 /g Sugar 4
Bi.sub.2 O.sub.3 Bismuth Ammonium Citrate, 400.degree. C 5.6
m.sup.2 /g Sugar 5 ZrO.sub.2 Zirconium Acetyl Acetate, 650.degree.
C 29.0 m.sup.2 /g Corn Syrup 6 Ta.sub.2 O.sub.5 Tantalum-Citric
Acid 600.degree. C 43.1 m.sup.2 /g Solution**, Sugar 7 Ta.sub.2
O.sub.5 Tantalum-Citric Acid 600.degree. C 108.4 m.sup.2 /g
Solution**, Sugar ______________________________________
*Ethylenediamine tetra-acetic acid. **Made by dissolving freshly
precipitated Ta.sub.2 O.sub.5 in a citric acid-hydrogen peroxide
mixture.
In each case, the desired oxide, free of detectable quantities of
second phases was obtained directly from ignition and identified by
analysis.
EXAMPLE 26
A further series of experiments were conducted in accordance with
the teachings of the previous examples to illustrate the
versatility of the invention in the manufacture of diverse mixed
oxides in highly reactive, high surface area forms. The results of
this series are summarized in Table II.
TABLE II
__________________________________________________________________________
Oxide Starting Materials Stoichiometry Surface Area
__________________________________________________________________________
1 CaSnO.sub.3 Stannous Acetate, Sugar, Calcium Acetate 1.19 40.5
m.sup.2 /g 2 CaSnO.sub.3 Stannous Tartrate dissolved in acetic acid
0.91 25.1 m.sup.2 /g solution, sugar, Calcium Acetate 3 CaSnO.sub.3
Stannous Acetate, Sugar, Calcium Acetate 0.84 15.1 m.sup.2 /g 4
Bi.sub.2 O.sub.3 . 2TiO.sub.2 Bismuth Ammonium Citrate, Sugar,
Tyzor TE* 1.96 10.3 m.sup.2 /g 5 Bi.sub.2 O.sub.3 . 2TiO.sub.2
Bismuth Ammonium Citrate, Sugar, Tyzor TE* 2.01 7.9 m.sup.2 /g 6
Bi.sub.2 O.sub.3 . 2TiO.sub.2 Bismuth Ammonium Citrate, Sugar,
Tyzor TE* 23.5 m.sup.2 /g 7 CaZrO.sub.3 Calcium Acetate, Corn
Syrup, Zirconium Nitrate 32.9 m.sup.2 /g 8 CaZrO.sub.3 Calcium -
EDTA Complex, Sugar, Zirconium 22.1 m.sup.2 /g Acetyl Acetate 9
CaZrO.sub.3 Zirconium Acetyl Acetate-Complex with 46.8 m.sup.2 /g
Triethanolamine, Sugar, Calcium Acetate 10 Nd.sub.2 O.sub.3 .
2TiO.sub.2 Neodymium Acetate, Sugar, Tyzor TE* 2.042 25.1 m.sup.2
/g
__________________________________________________________________________
*DuPont tradename for tetraethanolamine titanate in isopropyl
alcohol.
EXAMPLE 27
The purpose of this example was to demonstrate the preparation of
sub-micron size strontium hexaferrite powder. The solution used in
this example was prepared in the following way: 96.96g of hydrated
ferric nitrate and 6.88g of anhydrous strontium nitrate were
dissolved into 200cc of water. 200cc of corn syrup was added to and
thoroughly mixed with this solution. The resulting solution was
converted to a char by heating, and the char was then ignited at
400.degree. C in air. The resulting powder was characterized by
X-ray diffraction to be strontium ferrite. Specific surface area of
the powder was measured to equal 21.25 m.sup.2 /g.
EXAMPLE 28
The purpose of this example was to demonstrate the preparation of
sub-micron size strontium hexaferrite powder. The solution used in
this example was prepared from ferric nitrate and strontium nitrate
and was assayed to contain the equivalent of 11.23g/l of SrO and
99.31g/l of Fe.sub.2 O.sub.3. Its specific gravity was measured to
be 1.262g/cc.
Sheets of paper pulp were soaked for several hours in this
solution. The excess solution was then removed by subjecting the
wet sheets to centrifugation. The impregnated sheets of paper pulp
were then ignited in air by burning them in a tray. The resulting
powder was characterized by X-ray diffraction to be single phase
strontium ferrite. Specific surface area of the powder was measured
to equal 34.7 m.sup.2 /g. Crystallite size of the powder was
estimated from X-ray line broadening to be in the 900 A range.
EXAMPLE 29
The purpose of this example was to demonstrate the preparation of
sub-micron size barium hexaferrite powder. The solution used in
this example was prepared from ferric nitrate and barium nitrate,
and contained the equivalent of 42.75g/l of Fe.sub.2 O.sub.3 and
6.89g/l of BaO.
Sheets of paper pulp were soaked for several hours in this
solution. The excess solution was then removed by subjecting the
wet sheets to centrifugation. The impregnated sheets of paper pulp
were then ignited in air by burning them in a tray. The resulting
powder was characterized by X-ray diffraction to be single phase
barium ferrite. Specific surface area of the powder was measured to
equal 22.7 m.sup.2 /g.
EXAMPLE 30
The purpose of this example was to demonstrate the preparation of
sub-micron size W-phase ferrite powder - SrO. 2 MgO.8 Fe.sub.2
O.sub.3. The solution used in this example was prepared in the
following way: 981.5cc of ferric nitrate solution containing the
equivalent of 123.28g ferric oxide and 50cc of strontium nitrate
solution containing the equivalent of 19g strontium oxide were
mixed together. 50g of magnesium nitrate corresponding to 7.78g of
magnesium oxide was added and dissolved in this solution.
Sheets of paper pulp were soaked for several hours in the solution.
The excess solution was then removed by subjecting the wet sheets
to centrifugation. The impregnated sheets of paper pulp were then
ignited in air. A mild ignition was achieved by letting the sheets
burn in an open tray. The resulting powder was characterized by
X-ray diffraction to be composed of small crystallites of W-phase
ferrite. Specific surface area of the powder was measured to equal
46.54 m.sup.2.
EXAMPLE 31
The purpose of this example was to demonstrate the preparation of
sub-micron size barium hexaferrite powder. The solution used in
this example was prepared in the following way: 100g of ferrous
gluconate was dissolved in 500cc of warm water, 5.2g of barium
acetate was then added to and dissolved in the solution, 500cc of
corn syrup was then added to and thoroughly mixed with the
solution. The resulting solution was converted to a char by heating
and the char was then ignited at 600.degree. C in air. The
resulting powder was characterized by X-ray diffraction to be
single phase barium ferrite. Specific surface area of the powder
was measured to equal 39.6 m.sup.2 /g.
Although the invention has been illustrated by the preceding
examples, it is not to be construed as being limited to the
materials employed therein, but rather, the invention relates to
the generic area as hereinbefore disclosed. Various modifications
and embodiments thereof can be made without departing from the
spirit and scope thereof.
* * * * *